In an emulsion composition used in cosmetics and the like, an aqueous component and an oil-based component are stably mixed by emulsifying action of a surfactant contained in the composition.
However, a surfactant is a highly sticky material, and thus, as far as possible, reduction or exclusion of a surfactant is desired for preparing cosmetics having favorable feeling in use.
Under the above circumstances, various trials have been made to produce an emulsion composition without using a surfactant.
In the early 1900s, it was reported that mixing of powder particles or colloidal particles into two mutually immiscible liquids leads to adsorption of the particles onto the interface of the liquids, which resulted in stabilization of the resultant emulsion system. The emulsion produced by this method is referred to as a Pickering emulsion, and is widely used in various natural and industrial processes (see Non-Patent Literature 1). An application of the Pickering emulsion is also proposed in the cosmetic field. However, various restrictions (such as, size, noncohesiveness, and wettability) are imposed on available powders and colloidal particles, which leads to limitation of types of powders and colloidal particles applicable to cosmetics (see Patent Literatures 1 to 3).
Inorganic powder particles used in the Pickering emulsion (e.g., Patent Literature 1: polyalkyl silasesquioxane particles, Patent Literature 2: a metal oxide, Patent Literature 3: silica/titanium dioxide/zinc oxide, Patent Literature 4: an inorganic powder) generally have an emulsifying ability inferior to that of a surfactant widely used in cosmetics. Thus, a large amount of the powder should be added to the Pickering emulsion to achieve higher emulsion stability. As a result, the high concentration of the powder particles leads to creakiness and powderiness, which tends to result in impairment of fresh feeling. A Pickering emulsion containing spherical organic particles instead of inorganic powder particles as an emulsifying agent is also produced to solve the problem. However, more than a dozen percent, in total, of the spherical organic particles and an elastomeric organopolysiloxane should be added, and thus the problem relating to creakiness and powderiness is not sufficiently solved under current circumstances (see Patent Literature 5).